[RFC][Flang][driver] Try to support `flang -cc1as`

[sunshaoce]

Summary

Try to implment using flang -cc1as compile assembly files. Related patch (fc1as): https://reviews.llvm.org/D143478

[kiranchandramohan]

flang/tools/flang-driver/CMakeLists.txt

37–41

In general we are trying to limit or reduce the dependency on Clang. This will further increase the dependency. Can we share more code by moving the common portion to llvm/lib/Frontend?

[clementval]

flang/tools/flang-driver/CMakeLists.txt

37–41

+1

[awarzynski]

If this is all that's needed to have an integrated assembly in LLVM Flang, then this is good news and https://reviews.llvm.org/D143478 should be abandoned in favor of this approach. However, we need to find alternatives to increasing dependency on Clang.

flang/tools/flang-driver/CMakeLists.txt

37–41

+1

[sunshaoce]

Simplified code

flang/tools/flang-driver/CMakeLists.txt

37–41

I think this may need to deal with the TextDiagnosticPrinter part. But I don't have a good way to handle it yet.

[jsjodin]

@sunshaoce, @awarzynski are there remaining issues with this patch? We currently needs this for our testing.

[awarzynski]

In D143572#4192645, @jsjodin wrote:

@sunshaoce, @awarzynski are there remaining issues with this patch?

"However, we need to find alternatives to increasing dependency on Clang." ;-)

We should avoid code duplication, so making sure that flang-new -fc1as == clang -cc1as is a good thing. But the extra dependency on clangFrontend would be a step away from making Flang independent of Clang.

We currently needs this for our testing.

Presumably, this is only needed for compiling assembly files? Why not use clang --cc1as instead? At least as an interim solution.

[kiranchandramohan]

flang/tools/flang-driver/CMakeLists.txt

37–41

@DavidTruby Can you have a quick look whether we can refactor the case for TextDiagnosticPrinter?